RC vs CC again

[Richard Brekne]

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Farrell wrote:

>  Comments below - I need some clarification to address these issues.

Rather then copy over all this let me just re-word and see if that
helps.

A crowned CC panel, in addition to whatever else it is... is a curved
peice of wood. And as such the convex side will be stretched relative to
the concave side.  The overall levels of compression in the panel make
no difference in this regard. When downbearing is applied, then the
convex side will be compressed, and the concave side will stretch
relative to their condition before downbearing is applied. . But the
ribs resist this stretching tendancy, they will resist any stretching
tendancy on the part of the underside of the soundboard.

In otherwords... the underside of the panel tried to expand when it took
on humidity... the ribs resisted this and crown was induced and the ribs
were bent. Pushing down on the board will increase the panels pressure
on the ribs because the underside wants to expand even more.


     So as stated above, when you apply downbearing, yes, the
     concave side of the rib stretches, but only with reference to
     its curved compressed state - it doesn't stretch relative to
     when it was straight. I think it is more appropriate and more
     clear to state that when downbearing is applied, the concave
     side of the rib experiences a reduction of its compressed
     state.

Terry.. I think you misread something here out of what I was saying
...yes ??  Applying downbearing will stretch the concave side of the
panel.. the convex side of the rib will see this tendancy to expand just
as it sees any tendancy to expand on the part of the panels
underside.... it will resist the expansion. Hence the rib will
experience an increase in stress,... ergo it has to be supporting the
crown against downbearing.  Just because the the rib is a bit flatter,
and there is an apparent lessening of the compression in the lower half
of the rib,  doesnt mean we can ignore this increase in stress on the
rib as a whole... or what ?

I dont see at this point how we can get around that, except by refuting
that the underside of the panel will want to expand when down bearing is
applied... and I dont see how we can get there at all.

I hope I've made clear where I'm getting hung up accepting this "ribs
dont support crown against downbearing" position.

Cheers
RicB

--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html
http://www.hf.uib.no/grieg/personer/cv_RB.html


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